JEE Main & Advanced Sample Paper JEE Main Sample Paper-5

  • question_answer
    Which of the following compound does not formed during Lassaigne's test?

    A)  ferricferro cyanide        

    B)  ferricthiocyanide

    C)  silver chloride                  

    D)  ferric cyanide

    Correct Answer: D

    Solution :

     Idea This problem includes conceptual mixing of elemental detection by Lassaigne's test for various elements. To solve this problem students are advised to undergo in depth understanding of Lassaigne's test which involve detection of N/S, X etc/Prepare sodium extract and write the chemical reaction involved in elemental  detection and answer the correct choice. Organic compound \[\xrightarrow[Fused]{Na}\]sodium extract For nitrogen detection Sodium extract is taken and \[FeS{{O}_{4}}\] is added to it followed by few drops of \[FeC{{l}_{3}}\] resulting solution is acidified with cone, HCI Prussian blue colour appears due to formation of ferric ferrocyanide. \[NaCN+FeS{{O}_{4}}\xrightarrow[-N{{a}_{2}}S{{O}_{4}}]{{}}Fe{{(CN)}_{2}}\] \[4NaCN\] \[\underset{Ferric\,ferricyanide\,(blue\,colour)}{\mathop{\underset{F{{e}_{4}}[Fe{{(CN)}_{6}}]}{\mathop{N{{a}_{4}}[Fe\underset{\downarrow }{\mathop{{{(CN)}_{6}}}}\,]4FeC{{l}_{3}}}}\,}}\,\] Detection of sulphur When sodium extract is taken and \[FeC{{l}_{3}}\]is added to it, this lead to formation of ferric thiocyanide (blood red colouration). \[NaSCN\xrightarrow[{}]{FeC{{l}_{3}}}\underset{\begin{smallmatrix}  Ferric\,thiocyanide \\  \,\,\,\,\,\,\,\,\,\,\,\,(blood\,red) \end{smallmatrix}}{\mathop{Fe{{(SCN)}_{3}}}}\,\] Detection of chloride Sodium extract is taken, a solution of \[HN{{O}_{3}}\] is added to it followed by\[AgN{{O}_{3}}\]then we get a white precipitate of AgCI. \[NaCl+AgN{{O}_{3}}\xrightarrow[{}]{{}}\underset{\begin{smallmatrix}  White\,ppt. \\  (so\operatorname{lub}le\,in\,N{{H}_{4}}O) \end{smallmatrix}}{\mathop{\downarrow AgCl\downarrow }}\,+NaN{{O}_{3}}\] But \[Fe{{(CN)}_{3}}\]is never formed during Lassaigne's test. Hence, correct option is . TEST Edge Problem involving detection of element and characteristics property of element involved in chemical reaction may also be asked in general. So, students are advised to go through characteristic properties of compound obtained study of during chemical identification also.

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